Proceedings of the Second International Symposium on Fire Economics, Planning, and Policy: A Global View Forest Harvest Can Increase Subsequent Forest Fire Severity1 Carter Stone,2 Andrew Hudak,3 Penelope Morgan4 Abstract The USDA Forest Service is progressing from a land management strategy oriented around timber extraction towards one oriented around maintaining healthy forested lands. The healthy Forest Initiative promotes the idea of broadscale forest thinning and fuel treatments as an effective means for mitigating hazardous fuel conditions and, by extension, fire risk. Fuels mitigation is proactive while fire suppression is reactive and expensive. Costs associated with suppressing large wildfires, as occur in the western USA with annual regularity, are astronomical and routinely exceed fire suppression budgets. It is not difficult to demonstrate that treating forest fuels is more cost effective than suppressing forest fires on untreated lands. In addition, forest thinning is potentially profitable, or at least can recoup the cost of thinning, and may also produce safer conditions for those living in the wildland-urban interface zones. Thinning practices also facilitate wildland firefighting efforts for monitoring and controlling future fire incidents as well as for forest health management practices by state and federal forestry agencies. However, forest thinning and other fuel treatment strategies can take many different forms, some of which can do more harm than good when considered with other factors that influence wildfire behavior, such as weather and terrain. One example of this issue can be seen in Montana during the 2003 fires. At the Cooney Ridge fire complex, an extensively and homogeneously logged watershed burned severely and uniformly due to remaining ground slash (which had attained low fuel moisture after overstory removal) and severe fire weather (low relative humidity and strong upslope winds). This contrasted with a mosaic of burn severities in an adjacent watershed with higher fuel loads yet greater heterogeneity in fuel distribution at the stand and landscape levels. Harvesting timber does not translate simply into reducing fire risk. Given the stochastic nature of fire weather events, and the complex terrain of most forested landscapes in the western USA, applying a variety of forest thinning and fuel treatment operations towards the goal of maintaining a diverse forest habitat mosaic, also constitutes a sensible fire risk mitigation strategy. Introduction In recent decades, fires have burned an increasingly larger area in the western US. The many large fires experienced in the western US have been variously attributed to effective fire suppression that has allowed fuels to accumulate, to land use including logging that has removed larger trees but not always thinned the smaller tress that remain, and to climate change (Morgan and others 2003). In some drier forest types, 1An abbreviated version of this paper was presented at the second international symposium of fire economics, policy, and planning: a global view, 19–22 April, 2004, Córdoba, Spain. 2 GIS Analyst, University of Idaho Department of Forest Resources, Moscow, ID, USA. 3 Research Forester, USDA Forest Service Rocky Mountain Research Station, Moscow, ID, USA. 4 Professor, University of Idaho Department of Forest Resources, Moscow, ID, USA. 2 GENERAL TECHNICAL REPORT PSW-GTR-208 Proceedings of the Second International Symposium on Fire Economics, Planning, and Policy: A Global View Session 6A—Forest harvest Increase Fire Severity—Stone, Hudak, Morgan such as the semi-arid ponderosa pine ecosystems, tree density far exceeds historical norms and these can fuel unusually intense fires (Covington and others 2000). Elsewhere, however, many forests, such as sub-alpine forests at high elevations, naturally contain abundant surface and canopy fuels. There, intense and severe fires were the historical norm. The increasing number of people living in and using forests and rangelands have greatly increased both the chances of fires starting and the degree to which fires threaten people and their property when wildfires do occur. Dense thickets of younger trees now abound, and human and ecological communities are increasingly vulnerable to destructive crown fires. A consensus has emerged that it is urgent to restore more natural conditions to these forests (Allen and others 2002). Large, severe fire events account for a majority of the total area burned over time (Strauss and others 1989), as well as threats to people and their property (Maciliwain 1994). The US responded to increased cost and extent of western wildfires with the National Fire Plan (http://www.fireplan.gov/content/home/) in 2000 and more recently with The Healthy Forest Initiative (http://www.whitehouse.gov/infocus/healthyforests/). Both the National Fire Plan and the Healthy Forest Initiative seek to reduce fire hazard through active fuels management via logging and prescribed burning. Efforts are designed to complement continued fire suppression, assistance to local communities, and rehabilitation. Both efforts build on recent concern over declining forest health in the western US as a result of fire exclusion, land use change, and climate change. Past emphases in fire management have been on wildfire suppression and prescribed fire to reduce hazardous fuels following timber harvest and improve wildlife habitat. On the other hand, lightning fires have been allowed to burn in wilderness areas to restore natural process for over thirty years. It is only in the last five or six years that fire management has extensively used prescribed burning and mechanical fuel treatments to reduce hazardous fuel accumulations in non-wilderness areas (Long 2003). The degree to which mechanical treatments such as thinning will reduce the intensity and severity of subsequent fires is a subject of lively debate (Morrison and others 2000). Relatively few studies exist, and these mostly have focused on dry forests. Burn Severity Burn severity is broadly defined as the degree of ecosystem change induced by fire (Ryan and Noste 1985). Severe fires are those that result in great ecological changes (Rowe 1983, Ryan and Noste 1985, Moreno and Oeschel 1989, Schimmel and Granstrom 1996, De Bano and others 1998, Ryan 2002). Compared to low severity fires, vegetation recovery is slower, nutrient cycles are more altered, invasive species are more abundant, tree mortality is higher, and soil erosion is more likely to follow severe fires. Burn severity encompasses fire effects on both vegetation and surface soils (Ryan 2002, Ryan and Noste 1985, Key and Benson 2001). Burn severity is usually mapped from remote sensing data, to assess ecological effects and the degree to which post-fire rehabilitation is needed to reduce soil erosion and speed vegetation recovery (Parsons and Orlemann 2002). The US Forest Service (USFS) and other land management agencies employ remote sensing tools in an effort to efficiently and effectively manage fire-adapted ecosystems. Fire perimeter data for this paper came from Incident Command Geographic Information Systems (GIS) during and immediately after the fire. Fire severity classes came from 526 USDA Forest Service Gen. Tech. Rep. PSW-GTR-xxx. xxxx. Proceedings of the Second International Symposium on Fire Economics, Planning, and Policy: A Global View Session 6A—Forest harvest Increase Fire Severity—Stone, Hudak, Morgan a Burned Area Reflectance Classification (BARC) map provided by the USFS Remote Sensing Applications Center (RSAC). Cooney Ridge Fire Cooney Ridge is one of several large wildfire events that occurred during the active 2003 fire season in western Montana (Fig. 1). A prolonged drought of four years preceded a very dry summer, and the weather in late August was hot, dry and windy. On August 8, 2003, lightning ignited a fire on Cooney Ridge, located approximately 18 miles east of Missoula, Montana (Fig. 2). Despite intensive suppression efforts (www.fs.fed.us/r1/fire/2003fires), the Cooney Ridge fire burned 8589 ha before it was contained on October 15, 2003. Many people who lived in small towns and scattered homes in nearby valleys feared that this fire would spread toward them. The fire threatened industrial power lines serving eastern Washington, northern Idaho and western Montana. A world-famous trout fishing stream, Rock Creek, directly to the east (and downwind) of the fire, was another resource fire fighters sought to protect. Figure 1 — Aerial Photo of the Cooney Ridge Fire. Figure 2—Location of the Cooney Ridge Fire. The Cooney Ridge fire perimeter (Fig. 3) includes both public (54%) and private (46%) land. Most of the public land is managed by the USFS for multiple uses including timber extraction, recreation, and wildlife habitat, while only 177 ha (4%) 527 USDA Forest Service Gen. Tech. Rep. PSW-GTR-xxx. xxxx. GENERAL TECHNICAL REPORT PSW-GTR-208 Proceedings of the Second International Symposium on Fire Economics, Planning, and Policy: A Global View Session 6A—Forest harvest Increase Fire Severity—Stone, Hudak, Morgan is managed by the Montana Department of Fish and Game. Private land is mostly industrial forestland belonging to Plum Creek Timber Company, while only 48 ha (1%) is under other private ownership. Results Overall, 88% of the area within the final fire perimeter burned. More than 98% of private land burned, while 79% of public land burned. The areas that contain the most unburned vegetation are on the public lands portion (Table 1). Table 1—Area Burned on Public and Private Land in the 2003 Cooney Ridge Fire, Montana, USA. Private Public Class Hectares Percent (%) Hectares Percent (%) Un-Burned 83 2 984 21 Burned 3899 98 3622 79 Low 228 6 1347 29 Moderate 1704 43 1594 35 High 1967 49 681 15 Total 3982 100% 4607 100% 28 USDA Forest Service Gen. Tech. Rep. PSW-GTR-xxx. xxxx. Proceedings of the Second International Symposium on Fire Economics, Planning, and Policy: A Global View Session 6A—Forest harvest Increase Fire Severity—Stone, Hudak, Morgan Much more private land burned severely compared to public land (Fig. 4). Heavily logged areas and tree plantations have been known to burn more extensively than intact forests (Brown 2002).